This invention concerns a method and apparatus for sharpening the cutting edges of metal-cutting tools, and more particularly relates to a method for accurately sharpening a milling tool having a number of cutting edges in a circular cylindrical array, and apparatus for positioning said milling tool for sharpening.
Milling tools are extensively used for the machining of metal structures to desired shapes. The milling tool, generally fabricated of special alloy steel having a very high hardness, is an integral monolithic structure comprised of a spindle or shaft portion and a cutting head portion disposed at an extremity of said shaft portion and coaxial therewith. The cutting head is comprised of a core which is substantially a continuation of the shaft, and a number of flutes upraised from the core, the outermost extremities of said flutes having elongated cutting edges in parallel juxtaposition symmetrically disposed about the tool axis. The present invention is concerned specifically with those milling tools wherein the cutting edges which define the perimeter of the head are disposed in a circular cylindrical locus about the tool axis, said edges being either straight and parallel to the axis, or helically disposed to the axis. The diameter of the cylindrical perimeter of the cutting head will generally range from about 0.125" to 2.0".
The cutting edge is comprised of two surfaces which converge to a V-shaped apex. One of said surfaces may be considered to be the exterior surface, disposed on the outer periphery of the tool. The second surface, which may be considered to be the interior surface, is substantially radially oriented with respect to the shaft axis. The angle of the cutting edge or apex is between 88.degree. and 70.degree., and preferably between 86.degree. and 81.degree., the smaller angled cutting edges being used on workpiece substrates of greater hardness. The cutting edge angle may sometimes be expressed as the degrees of angle to which the exterior surface is cut back from its unsharpened or 90.degree. tangential state. In such manner of defining the angle of the cutting edge, values between 2.degree. and 20.degree. are the same as the values of 88.degree. to 70.degree. expressed above.
When the milling tool is rotated at high speed about the shaft axis, and the cutting edges are forcibly brought to bear against a metal workpiece of ordinary hardness, metal will be controllably removed from surfaces of the workpiece by a shearing type of cutting action. After extended use, the cutting edges lose their sharpness and require re-sharpening.
Sharpening is generally accomplished by contacting the outer surface of the cutting edges with a rapidly rotating abrasive wheel comprised of a composition containing alundum, carborundum, diamond or other materials having a hardness above 9.0 on the original Mohs Hardness Scale. In order to secure an accurate and uniform cutting edge angle, special holding and guiding equipment is required to precisely present the cutting edges to the abrasive wheel. Such equipment heretofore available for the precision sharpening of milling tools has required time-consuming manipulations and repeated adjustments to secure the sought cutting edge angle, and to compensate for factors such as the diameter of the cutting head.
It is accordingly an object of the present invention to provide an apparatus for the precision rapid sharpening of the cutting edges of a milling tool.
It is another object of this invention to provide an apparatus as in the foregoing object capable of easily accommodating milling tools having cutting heads of various diameter.
It is a further object of the invention to provide an apparatus of the aforesaid nature capable of adjustably producing an accurate, uniform cutting edge angle on cutting heads of various diameter.
It is a still further object of this invention to provide apparatus for positioning the cutting edges of a milling tool for sharpening, said apparatus having position-compensating means to accommodate milling tools of different diameters.
These objects and other objects and advantages of the invention will be apparent from the following description.